As the applications of the information technology are extended widely and quickly, more and more information technology devices are developed and under research. In order to make computer more easily to be operated and used by the operator, more sophisticated and compatible devices for data input and process are also manufactured successively for different computer systems, wherein the most popular devices for the input of tracing point are the cursor device (such as mouse) or the stylus device (such as pen) for a digitizer tablet system.
The well-known digitizer tablet system has several transducer/cursor devices in the form of mouse, puck or pen. In order to find the position of a mouse or a pen on the surface of the digitizer tablet; that is, to calculate the coordinates and the variation of coordinates in a two-dimensional space, one most popular technique in the prior arts is to use the technology of electromagnetic inductive. On the digitizer tablet according to this technique, a plurality of electromagnetic inductive loops are applied to induce the signal from mouse or pen and, by a signal processing circuit and an A/D converter to convert and sample the inducing signal, such that the coordinates of the mouse or pen on the active area of the digitizer tablet are decided, and also are other functions decided, such as: scrolling, clicking, or tracing, etc.
Please refer to FIG. 1, which is an illustration for the part of the electromagnetic inductive loops of the prior digitizer tablet disclosed in the U.S. Pat. Nos. 4,878,553 and 5,028,745. As shown in FIG. 1, which is a part of the inductive loops used by the prior digitizer tablet, wherein it includes the electromagnetic inductive loops from L1 to L5. All of the electromagnetic inductive loops L1˜L5 are belonged to a specific axis, and the covering range of the inductive loop L1 overlapping another two inductive loops L2, L3; that is, the range enclosed by an inductive loop contains the initial terminals of next two inductive loops and, in other words, the inductive loops L2, L3 are continuous loops to L1, and their covered ranges are overlapped partially. If the position of an pointer device on the active area of a digitizer tablet is P1, then the magnetic field that pointer device emitted on point P1 can be induced by the nearby loops, and the induced currents generated in these loops will be received by analog switches separately and respectively and, according to the magnitudes of these inducing signals, the coordinates of the point P1 is calculated and decided.
As shown in FIG. 1, as in partial scan, if the pointed position of the pointer device is within the loop range of the loop L3 then, for each loop L1 to loop L5, the scan procedures for the pointer device on point P1 on the active area of the digitizer tablet are to emit signals from inductive loops individually, which also receives its own emitted signals from the pointer device in receiving time slot; that is, the signal emitted from L1 will be induced by the pointer device and emitted the signal again from the pointer device and induced by L1, the signal emitted from L2 will be induced by the pointer device and emitted the signal again from the pointer device and induced by L2, the signal emitted from L3 will be induced by the pointer device and emitted the signal again from the pointer device and induced by L3, the signal emitted from L4 will be induced by the pointer device and emitted the signal again from the pointer device and induced by L4, and the signal emitted from L5 will be induced by the pointer device and emitted the signal again from the pointer device and induced by L5; the coordinates of point P1 where the pointer device is located will be calculated according to the magnitude of each signal emitted and induced by respective loops L1˜L5, such that the coordinates of the point P1 and the performed functions are decided. For this prior-art technique, since the coordinates of point P1 where the pointer device is located on the active area of the digitizer tablet is calculated by the signals emitting, inducing, and receiving respectively by each nearby loop of the point P1, the magnitudes of these signals are displayed as a nonlinear relationship. Therefore, this prior technique has the disadvantage that its coordinates calculation approach is too complicated and the number of the applied circuit elements used in coordinates calculating is too many relatively. As a result, the cost is higher and, in the other hand, its' inducing ability is less stable, and apt to couple the noise easily. It is very urgent to solve all these problems.
In addition, one prior-art wireless pointer device (such as stylus) used in the prior digitizer tablet according to the U.S. Pat. Nos. 4,878,553 and 5,028,745 utilizes a variable capacitor to the circuit which related the mechanism of the tip's movement, wherein the circuit is parallel with several paralleled capacitors (three capacitors), and the variable capacitor is brought along with the tip of the pointer device, and the key switch of the pointer device is utilized to parallel another capacitor. When operating the pointer device on the tablet surface or pressing it upon the surface of the digitizer tablet, the tip of the pointer device will press the variable capacitor and cause the capacitance change such that, after the pointer device processing a resonant energy storage to the signals coming from the digitizer tablet, the resonant frequency of the electromagnetic signals emitted back to digitizer tablet will be slightly changed, and this slight change of frequency is regarded as the phase variation (the greater is the pressure coming from the pointer device, the lower is the frequency and the greater is the phase variation). By detecting and processing the vibration of the phase and the amplitude of the electromagnetic signals transferred from the pointer device, the digitizer tablet may distinguish the pointer device is kept in touch with the surface of the digitizer tablet or within the inductive altitude of the digitizer tablet, and may also know which function the user is desired to perform in that time. When the user presses the key switch of the pointer device, it will make specific capacitor paralleled with resonant circuit, such that it will also cause the frequency of the electromagnetic signals resonated in the pointer device and transferred back to the digitizer tablet to be lowered down and the phase variation to be made greater and, by detecting the variation of phase, the digitizer tablet will be noticed which key switch the user has already pressed.
There are several disadvantages for this kind of prior-art technique that processes the resonant frequency (phase) of the pointer device by the manner of changing the capacitance:
(1) From this prior-art technique, the variation of the frequency by the manner of the “variable capacitor” with the tip of the pointer device so, when the pressure applied on the active area of the digitizer tablet by the tip of the pointer device is different, the capacitance of this resonant circuit (variable capacitor) will be enlarged slightly; that is, the variation of the frequency is not very much, so it is relatively difficulty to detect the magnitude of the pressure pressed on the active area of the digitizer tablet by the amount of the “frequency variation”. Therefore, for the prior-art technique that applies the manner of detecting the “phase change” difference of frequency to decide the pressure pressed by the tip, not only more precise measurement is required, but also the circuit design is complex and the production cost is increased.
(2) For this prior-art technique, no matter when the user presses the key switch of the pointer device or presses down the tip of the pointer device on the active area of the digitizer tablet, they will both cause the resonant frequency of the pointer device to be lowered down. In order to distinguish both operations of the pen tip and the key switch pressing for avoiding wrong judgment, this prior-art technique has a large range of each frequency variation generated from both the tip and the key switch pressing (frequency difference must be enlarged). Relatively, all the required accuracy and the complicity on the circuit design will be increased for distinguishing the frequency difference, and it is difficult to further lower down the cost either.